Today, we’d like to discuss the problem of magnesium oxide board joint crack.
What is mgo board?
A cost effective fire rated inorganic binded reinforced by glass mesh and plant fiber, roll into a flat sheet,that can be use for strucutal and non stuctural wall and subfloor.
Why mgo board joint crack more requently?
Moisture content
Gypsum board and fiber cement board have mature drying facility, moisture may 10-12% when export.However many mgo board supplier don’t have moisture control facility,result in uneven and excessive moisture when export,moisture may 10-25%.
Dry shrinkage
The dimension change of gypsum board and fiber cement board <0.15-0.3% test to EN and ASTM standard, mgo board is the same. However if you change temperature range 5-50’c, gypsum board and fiber cement board doesn’t change a lot, mgo board might have 0.3-0.6% dry shrinkage.
Environment
Laboratory test environment: stablize temperature, varying humidity. Acutal working environment: varying temperate and humidity.Compare with laboratory test result, there is bigger dimension change when the board suffer heavy rain in the morning,then extremely hot in the afternoon.GB33544 has wet expansion test for mgo board, however there is blind area for international market.
How to avoid mgo board joint crack?
1, Make sure of board moisture and environment
Mgo board might have larger dry shrinkage/wet expansion when it is too wet or too dry.
Mgo board might effect jointing compound curing when it is too dry, absorb moisture fast.
The board should adapt to environment 48 hours,make sure of moisture content 10-15% before plaster and joint.
2, Frame span:400mm – 600mm, frame thickness>0.7mm, screw span< 300mm
3, Recommend to use waterproof primer and flexible jointing compound.
Avoid wasting money on repair or rebuild, it’s better to purchase mgo board from certified supplier, because high quality mgo board have strict control of moisture and dry shrinkage <0.3%
We offer elastic jointing compound for mgo board at competitve price, please contact our sales for more details.